Re: [PATCH 2/2] perf pmu: Fix num_events calculation

[Ian Rogers <irogers@google.com>]

On Thu, May 9, 2024 at 11:52 PM Justin He <Justin.He@arm.com> wrote:
>
> Hi, Ian
>
> > -----Original Message-----
> > From: Ian Rogers <irogers@google.com>
> > Sent: Friday, May 10, 2024 2:17 PM
> > To: Justin He <Justin.He@arm.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>; Ingo Molnar <mingo@redhat.com>;
> > Arnaldo Carvalho de Melo <acme@kernel.org>; Namhyung Kim
> > <namhyung@kernel.org>; Mark Rutland <Mark.Rutland@arm.com>; Alexander
> > Shishkin <alexander.shishkin@linux.intel.com>; Jiri Olsa <jolsa@kernel.org>;
> > Adrian Hunter <adrian.hunter@intel.com>; Kan Liang
> > <kan.liang@linux.intel.com>; James Clark <James.Clark@arm.com>;
> > linux-perf-users@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH 2/2] perf pmu: Fix num_events calculation
> >
> > On Thu, May 9, 2024 at 7:47 PM Jia He <justin.he@arm.com> wrote:
> > >
> > > When pe is NULL in the function perf_pmu__new_alias(), the total
> > > number of events is added to loaded_json_aliases. However, if
> > > pmu->events_table is NULL and cpu_aliases_added is false, the
> > > calculation for the events number in perf_pmu__num_events() is incorrect.
> > >
> > > Then cause the error report after "perf list":
> > > Unexpected event
> > smmuv3_pmcg_3f062/smmuv3_pmcg_3f062/transaction//
> > >
> > > Fix it by adding loaded_json_aliases in the calculation under the
> > > mentioned conditions.
> > >
> > > Test it also with "perf bench internals pmu-scan" and there is no
> > > regression.
> > >
> > > Fixes: e6ff1eed3584 ("perf pmu: Lazily add JSON events")
> > > Signed-off-by: Jia He <justin.he@arm.com>
> > > ---
> > >  tools/perf/util/pmu.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c index
> > > a1eef7b2e389..a53224e2ce7e 100644
> > > --- a/tools/perf/util/pmu.c
> > > +++ b/tools/perf/util/pmu.c
> > > @@ -1639,6 +1639,8 @@ size_t perf_pmu__num_events(struct perf_pmu
> > *pmu)
> > >                  nr += pmu->loaded_json_aliases;
> > >         else if (pmu->events_table)
> > >                 nr +=
> > pmu_events_table__num_events(pmu->events_table,
> > > pmu) - pmu->loaded_json_aliases;
> > > +       else
> > > +               nr += pmu->loaded_json_aliases;
> >
> > Thanks for working on this! The "struct pmu_event *pe" in new_alias is an entry
> > from the json data, and "pmu->events_table" should NULL if there is no json
> > data. I believe the code is assuming that these lines aren't necessary as it
> > shouldn't be possible to load json data if the json events table doesn't exist for
> > the PMU - if there is no json data then loaded_json_aliases should be 0 and no
> > addition is necessary. I'm wondering why this case isn't true for you.
> On my Armv8a N2 server, "pmu->events_table" is NULL because perf_pmu__find_events_table()
> return NULL.
>
> I also noticed that pmu->loaded_json_aliases is *not* 0. The missing adding calculation will cause
> perf_pmu__num_events() less than normal case and will trigger latter check failure in
> perf_pmus__print_pmu_events__callback().
> At last, perf list will report many lines similar as:
> Unexpected event smmuv3_pmcg_3f062/smmuv3_pmcg_3f062/transaction//

The issue is the sys events which currently are ARM only. Here is an
lldb stack trace:
```
    frame #6: 0x0000aaaaabc9b49c
perf`__assert_fail(assertion="pmu->events_table",
file="tools/perf/util/pmu.c", line=522, function="int
perf_pmu__new_alias(struct perf_pmu *, const char *, const char *,
const char *, FILE *, const struct pmu_event *)")
    frame #7: 0x0000aaaaab41e018
perf`perf_pmu__new_alias(pmu=0x00007377e7e09b40,
name="hnf_brd_snoops_sent", desc="Counts number of multicast snoops
sent (not including SF back invalidation)", val="eventid=9,type=5",
val_fd=0x0000000000000000, pe=0x0000ffffffffde88) at pmu.c:522:3
    frame #8: 0x0000aaaaab4175cc
perf`pmu_add_sys_aliases_iter_fn(pe=0x0000ffffffffde88,
table=0x0000aaaaac299bb0, vdata=0x00007377e7e09b40) at pmu.c:939:3
    frame #9: 0x0000aaaaaaf6d000
perf`pmu_events_table__for_each_event_pmu(table=0x0000aaaaac299bb0,
pmu=0x0000aaaaac299238, fn=(perf`pmu_add_sys_aliases_iter_fn at
pmu.c:931), data=0x00007377e7e09b40) at pmu-events.c:5994:23
    frame #10: 0x0000aaaaaaf6cd78
perf`pmu_events_table__for_each_event(table=0x0000aaaaac299bb0,
pmu=0x0000000000000000, fn=(perf`pmu_add_sys_aliases_iter_fn at
pmu.c:931), data=0x00007377e7e09b40) at pmu-events.c:6057:23
    frame #11: 0x0000aaaaaaf6ec44
perf`pmu_for_each_sys_event(fn=(perf`pmu_add_sys_aliases_iter_fn at
pmu.c:931), data=0x00007377e7e09b40) at pmu-events.c:6295:27
    frame #12: 0x0000aaaaab41738c
perf`pmu_add_sys_aliases(pmu=0x00007377e7e09b40) at pmu.c:955:2
    frame #13: 0x0000aaaaab4179fc
perf`perf_pmu__lookup(pmus=0x0000aaaaac500970, dirfd=34,
name="arm_cmn_0") at pmu.c:1037:2
    frame #14: 0x0000aaaaab4242d0 perf`perf_pmu__find2(dirfd=34,
name="arm_cmn_0") at pmus.c:161:9
    frame #15: 0x0000aaaaab421614 perf`pmu_read_sysfs(core_only=false)
at pmus.c:209:3
    frame #16: 0x0000aaaaab42278c
perf`perf_pmus__scan_skip_duplicates(pmu=0x0000000000000000) at
pmus.c:297:3
    frame #17: 0x0000aaaaab422078
perf`perf_pmus__print_pmu_events(print_cb=0x0000ffffffffec68,
print_state=0x0000ffffffffecd0) at pmus.c:462:16
    frame #18: 0x0000aaaaab425d9c
perf`print_events(print_cb=0x0000ffffffffec68,
print_state=0x0000ffffffffecd0) at print-events.c:409:2
    frame #19: 0x0000aaaaab093ef0 perf`cmd_list(argc=0,
argv=0x0000fffffffff340) at builtin-list.c:592:3
    frame #20: 0x0000aaaaaaf5b490
perf`run_builtin(p=0x0000aaaaac4e8220, argc=1,
argv=0x0000fffffffff340) at perf.c:349:11
    frame #21: 0x0000aaaaaaf5a3e0 perf`handle_internal_command(argc=1,
argv=0x0000fffffffff340) at perf.c:402:8
    frame #22: 0x0000aaaaaaf5b1a0
perf`run_argv(argcp=0x0000fffffffff1c8, argv=0x0000fffffffff1c0) at
perf.c:446:2
    frame #23: 0x0000aaaaaaf59f44 perf`main(argc=1,
argv=0x0000fffffffff340) at perf.c:562:3
```

As such the fix here is incomplete. There may be both sys json events
(detected by PMU/id name) and CPU json events (detected by CPUID). I'm
looking into a fix.

Thanks,
Ian

> --
> Cheers,
> Justin (Jia He)